Chemical Equilibrium and Le Chatelier's Principle
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Questions and Answers

What occurs during dynamic equilibrium in a reversible reaction?

  • Only reactants are present in significant amounts.
  • The concentrations of reactants and products change continuously.
  • The forward and backward reactions occur at equal rates. (correct)
  • The reaction ceases to change at any point.

    • In which direction does the equilibrium shift when the temperature is increased for an exothermic reaction?

  • There is no effect on the equilibrium position.
  • The equilibrium shifts towards the reactants. (correct)
  • The equilibrium shifts equally in both directions.
  • The equilibrium shifts towards the products.

    • What does the position of equilibrium indicate?

  • The proportions of reactants and products in the equilibrium mixture. (correct)
  • The rates of the forward reaction and reverse reaction are unequal.
  • The reaction will eventually go to completion.
  • The reaction has completely stopped.

    • What principle can be used to predict how changes in external conditions affect equilibrium?

    <p>Le Chatelier's Principle. (A)</p> Signup and view all the answers

    What would likely happen to the yield of ammonia if the temperature is decreased?

    <p>The yield of ammonia will increase. (C)</p> Signup and view all the answers

    If a reaction is described as shifting 'towards the left', what does this imply?

    <p>The concentration of reactants increases. (A)</p> Signup and view all the answers

    What happens to the equilibrium position if external pressure is increased?

    <p>It may shift towards the side with fewer moles of gas. (D)</p> Signup and view all the answers

    Which of the following statements is true regarding an endothermic reaction and temperature changes?

    <p>Increasing temperature favors the forward reaction. (A)</p> Signup and view all the answers

    What is the effect of increasing temperature on the yield of ammonia in an exothermic reaction?

    <p>Decrease the yield of ammonia by shifting equilibrium left (A)</p> Signup and view all the answers

    How does increasing pressure affect the equilibrium of the reaction CO(g) + 2H2(g) ⇌ CH3OH(g)?

    <p>Shifts equilibrium to the right, increasing methanol yield (B)</p> Signup and view all the answers

    What is the effect of decreasing pressure on a reaction with more moles of gas on the reactants' side?

    <p>Shifts equilibrium right, increasing products' yield (A)</p> Signup and view all the answers

    What temperature conditions typically yield both a reasonable yield and reaction rate?

    <p>Compromise temperatures for balanced yield and rate (A)</p> Signup and view all the answers

    What happens to the equilibrium if the concentration of OH- ions is increased?

    <p>Equilibrium shifts to the right to reduce OH- ions (D)</p> Signup and view all the answers

    Why is high pressure costly and often avoided in industrial processes?

    <p>Requires expensive high-energy equipment and pumping costs (A)</p> Signup and view all the answers

    In a reaction where the number of moles of gas on both sides is identical, what is the effect of changing pressure?

    <p>Has no effect on the equilibrium position (B)</p> Signup and view all the answers

    What does a high temperature do to an exothermic reaction's equilibrium?

    <p>Shifts equilibrium towards the reactant side (A)</p> Signup and view all the answers

    What happens to the position of equilibrium when H+ ions are added?

    <p>Equilibrium shifts back to the left, restoring the brown color (A)</p> Signup and view all the answers

    What is the role of a catalyst in a chemical equilibrium?

    <p>It speeds up the rate at which equilibrium is achieved without affecting its position (A)</p> Signup and view all the answers

    Which of the following pairs indicates the correct conditions for the Haber process?

    <p>Temperature of 450oC and pressure of 200-1000 atm (B)</p> Signup and view all the answers

    In the hydration of ethene to produce ethanol, what are the optimal conditions?

    <p>Temperature of 300oC, pressure of 70 atm, catalyst of conc H3PO4 (D)</p> Signup and view all the answers

    Why is high pressure used in the Contact process?

    <p>It improves both yield and reaction rate (A)</p> Signup and view all the answers

    What is the major consequence of using too high a pressure in industrial processes?

    <p>Excessive energy costs for pumps (C)</p> Signup and view all the answers

    What effect does lowering the temperature have on the yield in exothermic reactions?

    <p>It can increase the yield but may slow down the reaction rate (B)</p> Signup and view all the answers

    In terms of the equilibrium shift for the reaction producing SO2 in the Contact process, what does the addition of O2 do?

    <p>It shifts equilibrium to the right, favoring products (B)</p> Signup and view all the answers

    What is the effect of catalysts on the rate of reaction and equilibrium?

    <p>Catalysts increase the rate without affecting the equilibrium. (A)</p> Signup and view all the answers

    Which statement correctly summarizes the impact of high pressure in chemical reactions?

    <p>High pressure leads to unwanted polymerization and high energy costs. (C)</p> Signup and view all the answers

    What effect does recycling unreacted reactants have on the overall yield of a chemical process?

    <p>It can improve the overall yields of the processes. (B)</p> Signup and view all the answers

    When calculating the equilibrium constant Kc, which components are excluded from heterogeneous Kc expressions?

    <p>Solid and liquid concentrations. (D)</p> Signup and view all the answers

    For the equilibrium reaction H2(g) + Cl2(g) ⇌ 2HCl(g), if the concentrations at equilibrium are 0.67 mol dm-3 for H2 and 0.83 mol dm-3 for Cl2, what is the Kc expression for this reaction?

    <p>Kc = [HCl]^2 / ([H2][Cl2]) (C)</p> Signup and view all the answers

    Which parameter, if too high, could lead to excessive energy costs in a chemical process involving high pressure?

    <p>Pressures used to create the reaction. (B)</p> Signup and view all the answers

    In which scenario would using low temperature be beneficial, despite the slow reaction rate?

    <p>When achieving high product yield is critical. (B)</p> Signup and view all the answers

    What is the significance of stoichiometric balancing in the Kc expression?

    <p>It defines the ratio of products to reactants in equilibrium. (C)</p> Signup and view all the answers

    Study Notes

    Chemical Equilibrium

    • Chemical reactions can be reversible and reach a dynamic equilibrium where the forward and backward reactions occur at equal rates.
    • The concentrations of reactants and products remain constant in dynamic equilibrium.
    • The position of equilibrium describes the composition of the equilibrium mixture.
      • Favoring reactants means the mixture contains mostly reactants.

    Le Chatelier's Principle

    • Le Chatelier's principle predicts how changing conditions affect equilibrium.
    • If a change is made to a system at equilibrium, the system will shift to counteract that change.

    Temperature Effects

    • Increasing temperature shifts the equilibrium toward the endothermic direction to absorb the heat. This reduces the system's temperature.
    • Decreasing temperature shifts the equilibrium toward the exothermic direction to release heat, increasing the system's temperature.

    Pressure Effects

    • Increasing pressure shifts the equilibrium to the side with fewer moles of gas. This reduces the pressure.
    • Decreasing pressure shifts the equilibrium to the side with more moles of gas. This increases the pressure.
    • If the number of moles of gas is the same on both sides, pressure changes have no effect.

    Concentration Effects

    • Increasing the concentration of a reactant shifts the equilibrium to the right to consume the added reactant.
    • Increasing the concentration of a product shifts the equilibrium to the left to decrease the product concentration.

    Catalyst Effects

    • Catalysts speed up both the forward and backward reactions equally, not shifting the equilibrium.

    Equilibrium Constant (K)

    • K is a numerical value representing the equilibrium position.
    • K is calculated from the equilibrium concentrations of products and reactants, raised to their stoichiometric powers.
    • K only changes with temperature.
    • A larger K value indicates a greater product concentration at equilibrium.
    • K values are unitless for homogeneous systems.

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    Description

    Explore the fascinating concepts of chemical equilibrium, including reversible reactions and dynamic equilibrium. This quiz delves into Le Chatelier's principle and how changes in temperature and pressure affect equilibrium conditions. Test your understanding of these fundamental principles in chemistry.

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